Wavelength conversion device, manufacturing method thereof, and related illumination device

ABSTRACT

A wavelength conversion device, a manufacturing method thereof, and a related illumination device. The wavelength conversion device comprises a fluorescent powder layer ( 110 ) that is successively stacked, a diffuse reflection layer ( 120 ), and a high-thermal-conductivity substrate ( 130 ). The diffuse reflection layer ( 120 ) comprises white scattered particles for scattering the incident light; the high-thermal-conductivity substrate ( 130 ) is one of an aluminum nitride substrate, a silicon nitride substrate, a silicon carbide substrate, a boron nitride substrate, and a beryllium oxide substrate. The wavelength conversion device has good reflectivity and thermal stability.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to illumination and display technologies, and inparticular, it relates to a wavelength conversion device, amanufacturing method thereof, and a related light emitting device.

Description of Related Art

Using laser or LED as a light source to excite a phosphor material toobtain monochromatic light or polychromatic light is a widely usedtechnology in illumination, projection and other application fields.Such technologies typically direct a light emitted by the laser or LEDonto a phosphor color wheel which rotate at a high speed, to achievegood heat dissipation.

Color wheels in existing technologies include a two layer structure,where the lower layer is an aluminum substrate with a mirror surface,and the upper layer is a phosphor layer over the aluminum substrate.

The mirror-surface aluminum substrate primarily functions to reflectlight and conduct heat. The mirror-surface aluminum substrate istypically constructed of a three-layer structure: an aluminum base, ahigh reflectivity layer, and a surface dielectric protection layer. Thehigh reflectivity layer typically uses a high purity aluminum or highpurity silver, and a dielectric layer is coated on the high reflectivitylayer. The dielectric layer is formed of low refractive index materialMgF₂ or SiO₂ and high refractive index material TiO₂, and functions toprotect the high purity aluminum or high purity silver and to enhancereflectivity. This type of mirror-surface aluminum plate has twoproblems. First, the thermal expansion coefficients of the surfacedielectric protection layer and the high reflectivity layer do notmatch, so the dielectric protection layer tends to be damaged during thestamping process, or even fall off. Second, for the high reflectivitysilver layer which has a higher reflectivity, under high temperature, agap may form between the dielectric protection layer and the highreflectivity layer, so that the high reflectivity layer comes intocontact with the air; the silver atoms tend to react with the hydrogensulfide or oxygen in the air in a sulfidation or oxidation reaction,which results in drastic reduction in the reflectivity and thermalstability of the high reflectivity layer. For an aluminum reflectivelayer, the thermal stability of aluminum is better than silver, but itsreflectivity is not high enough. Therefore, under current fabricationconditions, mirror-surface aluminum substrate cannot withstand hightemperature, and is not suitable for high power light emitting devices.

SUMMARY

Embodiments of the present invention provide a high temperatureresistant wavelength conversion device, its manufacturing method, andrelated light emitting device.

An embodiment of the present invention provides a wavelength conversiondevice, which includes:

A phosphor layer, which includes a phosphor powder; A diffuse reflectionlayer, which includes white scattering particles for scattering anincident light;

A high thermal conductivity substrate, which is selected from: analuminum nitride substrate, a silicon nitride substrate, a siliconcarbide substrate, a boron nitride substrate, and a beryllium oxidesubstrate;

Wherein the phosphor layer, the diffuse reflection layer and the highthermal conductivity substrate are stacked sequentially and affixed toeach other.

Preferably, the thermal conductivity of the high thermal conductivitysubstrate is greater than or equal to 100 W/mK.

Preferably, the diffuse reflection layer further includes a first glasspowder for adhering the white scattering particles.

Preferably, the phosphor layer further includes a second glass powderfor adhering the phosphor powder.

Preferably, the white scattering particles include at least one of:barium sulfate particles, aluminum oxide particles, magnesium oxideparticles, titanium oxide particles, and zirconium oxide particles.

Preferably, the diffuse reflection layer includes a first glass powderfor adhering the white scattering particles, wherein the first glasspowder and the second glass powder are the same high melting point glasspowder.

Another embodiment of the present invention provides a light sourcedevice which includes the above described wavelength conversion device,and further includes an excitation light source for generating anexcitation light, wherein the phosphor powder absorbs the excitationlight to generate a converted light, and wherein the diffuse reflectionlayer scatter-reflects the converted light or a mixed light of theconverted light and unabsorbed excitation light.

Another embodiment of the present invention provides a manufacturingmethod for a wavelength conversion device, which includes:

A. Obtaining a high thermal conductivity substrate, which is selectedfrom: an aluminum nitride substrate, a silicon nitride substrate, asilicon carbide substrate, a boron nitride substrate, and a berylliumoxide substrate;

B. Obtaining a diffuse reflection layer, which includes white scatteringparticles for scattering an incident light;

C. Obtaining a phosphor layer, which includes a phosphor powder; and D.Sequentially stacking the phosphor layer, the diffuse reflection layerand the high thermal conductivity substrate and affixing them to eachother.

Preferably, step B and step D include:

Sintering the diffuse reflection layer on a surface of the high thermalconductivity substrate, wherein the diffuse reflection layer includeswhite scattering particles and a first glass powder, wherein thesintering temperature is lower than the melting point of the highthermal conductivity substrate, and affixing the phosphor layer on thesurface of the diffuse reflection layer on the surface of the substrate.

Preferably, step B, step C and step D include:

Sintering the diffuse reflection layer on a surface of the high thermalconductivity substrate, wherein the diffuse reflection layer includesthe white scattering particles and a first glass powder, wherein thesintering temperature is lower than the melting point of the highthermal conductivity substrate, and sintering the phosphor layer on thesurface of the diffuse reflection layer on the surface of the substrate,wherein the phosphor layer includes a second glass powder and thephosphor powder, and wherein the sintering temperature is T3≤Tf+400° C.,where Tf is the softening point of the first glass powder.

Preferably, the step of sintering the diffuse reflection layer on thesurface of the high thermal conductivity substrate includes:

B1. Obtaining the white scattering particles, the first glass powder,and an organic carrier;

B2. Mixing the white scattering particles, the first glass powder, andthe organic carrier to obtain a slurry of the scattering particles;

B3. Coating the slurry of the scattering particles over the high thermalconductivity substrate; and

B4. Sintering the high thermal conductivity substrate which has beencoated with the slurry of the scattering particles to obtain the diffusereflection layer.

Preferably, the step of sintering the phosphor layer on the surface ofthe diffuse reflection layer on the surface of the substrate includes:

C1. Obtaining the second glass powder, the phosphor powder, and anorganic carrier;

C2. Mixing the second glass powder, the phosphor powder, and the organiccarrier to obtain a slurry of the phosphor powder;

C3. Coating the slurry of the phosphor powder over the surface ofdiffuse reflection layer of the high thermal conductivity substrate; and

C4. Sintering the high thermal conductivity substrate which has beencoated with the slurry of the phosphor powder to obtain the phosphorlayer, wherein the sintering temperature is T3≤Tf+400° C., where Tf isthe softening point of the first glass powder.

Preferably, the process includes, between step B3 and step B4: heatingthe high thermal conductivity substrate which has been coated with theslurry of the scattering particles at a temperature T1 for over 0.2hours, wherein Tb−100° C.≤T1≤Tb+200° C., where Tb is the complete breakdown temperature of the organic carrier.

Compared with conventional technologies, the embodiments of the presentinvention have the following advantages:

In embodiments of the present invention, the wavelength conversiondevice uses a diffuse reflection layer and a high thermal conductivitysubstrate to replace the mirror-surface aluminum substrate of theconventional technology. The diffuse reflection layer includes whitescattering particles, which can scatter incident light, so that themirror reflection of the conventional metal reflective layer is replacedwith a diffuse reflection process to achieve reflection of the incidentlight. Moreover, even at high temperature, the white scatteringparticles will not be oxidized and become absorbent of the incidentlight. Therefore, even at high temperature, the diffuse reflection layerwill not have reduced reflectivity, making the device high temperatureresistant. Meanwhile, because the high thermal conductivity substrate isone of aluminum nitride, silicon nitride, silicon carbide, boronnitride, and beryllium oxide, the melting points of these ceramicmaterials are much higher than that of metal aluminum, so they canwithstand higher temperature than aluminum. As a result, the wavelengthconversion device according to embodiments of the present invention canwithstand high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a schematically illustrates the structure of a wavelengthconversion device according to an embodiment of the present invention;

FIG. 1b illustrates relative light emission intensity curves ofwavelength conversion devices using a mirror-surface aluminum substrateand using an aluminum nitride ceramic substrate, respectively, underdifferent excitation light powers;

FIG. 1c illustrates relative light emission intensity curves ofwavelength conversion devices using phosphor powder layer sealed withsilica gel and using phosphor powder sealed with glass powder,respectively, under different excitation light powers;

FIG. 2 is a flow chart of a manufacturing process for a wavelengthconversion device according to another embodiment of the presentinvention;

FIG. 3 is a flow chart of a manufacturing process for a wavelengthconversion device according to another embodiment of the presentinvention; and

FIG. 4 is a flow chart of a manufacturing process for a wavelengthconversion device according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention are described below with referenceto the drawings.

Refer to FIG. 1a , which schematically illustrates the structure of awavelength conversion device according to an embodiment of the presentinvention. As shown in FIG. 1a , the wavelength conversion deviceincludes a phosphor layer 110, a diffuse reflection layer 120, and ahigh thermal conductivity substrate 130, which are sequentially stackedand affixed together.

The phosphor layer 110 includes a phosphor powder. The phosphor powderabsorbs an excitation light and is excited by it to generate a convertedlight having a wavelength different from that of the excitation light.For example, YAG (yttrium aluminium garnet) phosphor can absorb blue andUV excitation light to generate a yellow converted light. The phosphorpowder may also be a red phosphor, a green phosphor, etc.

The diffuse reflection layer 120 reflects the incident light. Itincludes white scattering particles. The white scattering particles aretypically a salt or oxide powder, such as barium sulfate powder,aluminum oxide powder, magnesium oxide powder, titanium oxide powder,zirconium oxide powder, etc., which absorbs virtually no light.Moreover, the white scattering materials have stable properties and donot oxidize at high temperature. Considering that the diffuse reflectionlayer should have a good heat dissipation effect, preferably, analuminum oxide powder which has relatively high thermal conductivity isused. Of course, to accomplish the reflection of the incident light bythe diffuse reflection layer 120, the white scattering material in thediffuse reflection layer 120 should have sufficient compactness andthickness, which can be determined through experimentation.

Although metals have high thermal conductivity, when the temperature ofa metal exceeds a half of its melting point, the metal plate may deformdue to the temperature. For example, aluminum plate, steel plate, copperplate, etc., in particular when they are used as a substrate for forminga high melting point glass (glass with a softening point over 500° C.),tend to deform. Therefore, the high thermal conductivity substrate 130may be formed of a ceramic material having a thermal conductivitygreater than or equal to 100 W/mK, so that they can withstand relativelyhigh temperature while realizing high thermal conductivity. This typesof high thermal conductivity substrates are typically ceramic plateswith compact structures, such as aluminum nitride, silicon nitride,boron nitride, beryllium oxide, etc. Further, although the thermalconductivity of silicon carbide is only 80 W/mK, experiments show thatit can also be used as a high thermal conductivity substrate. Themelting points of these high thermal conductivity substrates are allabove 1500° C., much higher than the melting point of aluminum (700°C.), so they can withstand relatively high temperatures.

The wavelength conversion device uses the diffuse reflection layer andthe high thermal conductivity substrate to replace the mirror-surfacealuminum substrate of the conventional technology. The diffusereflection layer includes white scattering particles for scattering theincident light, so that the mirror reflection of the conventional metalreflective layer is replaced with a diffuse reflection process toachieve reflection of the incident light. Moreover, even at hightemperatures, the white scattering particles will not be oxidized andbecome absorbent of the incident light. Therefore, even at hightemperature, the diffuse reflection layer will not have reducedreflectivity, making the device high temperature resistant. Also,because the high thermal conductivity substrate is one of aluminumnitride, silicon nitride, silicon carbide, boron nitride, and berylliumoxide, they can withstand higher temperatures than aluminum. As aresult, the wavelength conversion device according to embodiments of thepresent invention can withstand high temperatures.

In one example, aluminum nitride ceramic is used as the substrate and analuminum oxide powder of 0.2 mm is disposed on its surface to form thediffuse reflection layer, where the particle diameter distribution ofthe aluminum oxide powder is between 0.2 μm to 0.5 μm, and the massratio of the aluminum oxide powder with the adhesive is 6:1. Themeasured reflectivity of such a diffuse reflection layer is 99.5% ofthat of the mirror-surface aluminum substrate, i.e., almost identical tothat of the mirror-surface aluminum substrate. Of course, the particlediameters of the diffuse reflection particles, the thickness of thediffuse reflection layer and its compactness can be other values, whichcan be obtained by those skilled in the art through routineexperimentation.

A phosphor layer is disposed on the surface of the above describeddiffuse reflection layer to obtain the wavelength conversion device.Under the illumination of an excitation light with a maximum power of 14W, a wavelength conversion device using a mirror-surface aluminumsubstrate and a wavelength conversion device using the above describedaluminum nitride ceramic substrate both receive the incident excitationlight, and the phosphor layers of both wavelength conversion devices aresealed with a silica gel. FIG. 1b illustrates relative light emissionintensity curves of the wavelength conversion devices using amirror-surface aluminum substrate and using an aluminum nitride ceramicsubstrate, respectively, under different excitation light powers. Asshown in FIG. 1b , the horizontal axis is the excitation light power,which has a maximum power of 14 W as stated above; the vertical axis isthe relative light emission intensity of the converted light generatedby the wavelength conversion device. As the excitation light powerincreases, the relative light emission intensity of the wavelengthconversion device using mirror-surface aluminum substrate increasesgradually. But when the excitation light power increases to above 30% ofthe maximum power, on the wavelength conversion devices using themirror-surface aluminum substrate, the silica gel of the phosphor layerdecomposes due to high temperature and becomes dark, causing therelative light emission intensity of the wavelength conversion device todecrease. Moreover, as the excitation light power increases further, thedecomposition of the silica gel is more severe, and the relative lightemission intensity drops even more. On the other hand, for thewavelength conversion device using the aluminum nitride ceramicsubstrate, in the initial stage, its relative light emission intensityincreases gradually as the excitation light power increases. When theexcitation light power increases to above 70% of the maximum power, thiswavelength conversion devices experiences the darkening of the silicagel of the phosphor layer, causing the relative light emission intensityof the wavelength conversion device to decrease; but its rate ofdecrease of the relative light emission intensity is slower than that ofthe wavelength conversion device using the mirror-surface aluminumsubstrate.

For mirror-surface aluminum substrate, its surface is relatively smooth;after the phosphor layer is formed on the surface of the mirror-surfacealuminum substrate, the contact surface of the phosphor layer with thesubstrate will contract, and partially separate form the substrate.Thus, the contact surface area of the phosphor layer with themirror-surface aluminum substrate is relatively small, and the thermalresistance of the interface between the phosphor layer and themirror-surface aluminum substrate is relatively large. On the otherhand, for the wavelength conversion device using the aluminum nitrideceramic substrate, because the surface of both the ceramic substrate andthe diffuse reflection layer are relatively rough, the contact surfaceareas between the phosphor layer and the diffuse reflection layer andbetween the diffuse reflection layer and the ceramic substrate arerelatively large, so that the interfacial thermal resistance of theformed wavelength conversion device is relatively small. Therefore, theheat generated by the phosphor layer can be better conducted to theceramic substrate, so that the wavelength conversion device canwithstand higher temperature.

In this embodiment, the wavelength conversion device uses a diffusereflection layer and a high thermal conductivity substrate to replacethe mirror-surface metal substrate of the conventional technology. Thediffuse reflection layer includes white scattering particles, which canscatter incident light, so that the mirror reflection of theconventional metal reflective layer is replaced with a diffusereflection process to achieve reflection of the incident light.Moreover, even at high temperature, the white scattering particles willnot be oxidized and become absorbent of the incident light. Therefore,the diffuse reflection layer can withstand high temperature. Also,because the high thermal conductivity substrate is at least one ofaluminum nitride, silicon nitride, silicon carbide, boron nitride, andberyllium oxide, the melting points of these ceramic materials are muchhigher than those of metals, so they can withstand higher temperaturethan metal. Also, although the thermal conductivities of these ceramicsubstrates are slightly lower than that of an aluminum substrate, theyare still higher than those of iron and some other metals. Moreover, theinterfacial thermal resistance between the high thermal conductivitysubstrate and the diffuse reflection layer and between the diffusereflection layer and the phosphor layer is relatively low, so the heatgenerated by the phosphor layer can be conducted to the ceramicsubstrate and dissipated into the air, which improves the thermalstability of the wavelength conversion device. Therefore, the wavelengthconversion device of this embodiment can take into consideration boththe reflectivity and thermal stability of the wavelength conversiondevice.

In practice, the phosphor powder is typically sealed by and adhesiveinto an integral mass. A typical adhesive is silica gel, which hasstable chemical properties and a high mechanical strength. However, asmentioned earlier, silica gel can withstand relatively low temperatures,typically between 300° C. and 500° C. For use in high power lightemitting devices, preferably, an inorganic adhesive is used to adherethe phosphor powder into an integral mass. The inorganic adhesive may besodium silicate, glass powder, etc., to achieve a high temperatureresistant reflective type phosphor wheel.

Preferably, the adhesive of the phosphor layer 110 is a second glasspowder. Glass powder is an irregularly shaped, particulate, homogeneousglass substance, which is highly transparent and has stable chemicalproperties. The second glass powder and the phosphor powder can beformed by sintering, so that the binding force between the phosphorlayer 110 and diffuse reflection layer 120 is very strong, and theformed phosphor layer 110 is highly transparent and also temperatureresistant.

For example, FIG. 1c illustrates relative light emission intensitycurves of wavelength conversion devices using phosphor powder layersealed with silica gel and using phosphor powder layer sealed with glasspowder, respectively, under different excitation light powers. Thesubstrates in both cases are aluminum nitride ceramic substrates. Asshown in FIG. 1, the horizontal axis is the excitation light power,which has a maximum power of 14 W, and the vertical axis is the relativelight emission intensity of the converted light. For the wavelengthconversion device using a silica gel seal, when the excitation lightpower increases to above 70% of the maximum power, the silica gel of thephosphor layer becomes dark, causing the relative light emissionintensity of the wavelength conversion device to decrease. Whereas forthe wavelength conversion device using a glass powder seal, because thesoftening point of the glass powder is relatively high and it does notbecome dark, when the excitation light power increases, the relativelight emission intensity of the wavelength conversion device increasesapproximately linearly.

Similarly, the white scattering particles also need to be adhered intoan integral mass using an adhesive. The adhesive may likewise be silicagel, sodium silicate, etc. Preferably, the white scattering particlesare adhered by a first glass powder. Here, the first glass powder may bethe same glass powder as the second glass powder, or different ones. Inthe diffuse reflection layer, the first glass powder adheres the whitescattering particles together, and insulates them form the air, toprevent them from becoming damp due to humidity in the air, and to givethe diffuse reflection layer relatively high strength and lighttransmission rate. Further, when the adhesives for both the phosphorlayer 110 and the diffuse reflection layer 120 are glass powders, thephosphor layer 110 can be sintered on the surface of the diffusereflection layer 120, or the diffuse reflection layer 120 can besintered on the surface of the phosphor layer 110, so that the bindingforce between the two is strong.

It should be noted that in a process where the diffuse reflection layer120 is formed first and then the phosphor layer 110 is sintered on thesurface of the diffuse reflection layer 120, when sintering the phosphorlayer 110, damage to the diffuse reflection layer 120 should be avoided.It is easy to understand that, when the sintering temperature T3 islower than the softening point of the first glass powder, the firstglass powder will not soften during the forming of the phosphor layer110, so the diffuse reflection layer 120 will not be impacted. But itwas discovered through experiments that, even when the sinteringtemperature T3 is higher than the softening point of the first glasspowder, so long as the fluidity of the first glass powder is not toohigh, damage to the diffuse reflection layer can be avoided. To ensurethat during the sintering of the phosphor layer 110 the fluidity of thesoftened first glass is not too high, it has been shown by experimentsthat the sintering temperature T3 should satisfy the followingcondition: T3≤Tf+400° C., where Tf is the softening point of the firstglass powder.

Similarly, if the phosphor layer 110 is formed first and then thediffuse reflection layer 120 is sintered on the surface of the phosphorlayer 110, the sintering temperature T3 should satisfy the followingcondition: T3≤Tf+400° C., where Tf is the softening point of the secondglass powder.

Actually, the first glass powder and the second glass powder may be thesame glass powder; as long as the sintering temperature of the secondsintering step is controlled in the above described manner, damage tothe first sintered diffuse reflection layer 120 or phosphor layer 110can be avoided. Thus, the two sintering steps can even use the sametemperature. For example, the first glass powder and the second glasspowder may both be high melting point glass powder, such as silicateglass powder. Compared to low melting point glass powder, high meltingpoint glass powder has better transparency, which can reduce light loss.

In the diffuse reflection layer 120 and phosphor layer 110, the firstglass powder and the second glass powder need to transmit incident lightwell, and also need to conduct heat well. Thus, preferably, the firstglass powder and/or the second glass powder are borosilicate glasspowder. Borosilicate glass powder has stable properties and hightransparency; compared to other glass powder, it also has high thermalconductivity. Moreover, because the softening point of the first glasspowder and the second glass powder should be different, and borosilicateglass powder has a relatively high softening point, this glass powdercan be used as the one of the first and second glass powders that isrequired to have a higher softening point.

The main function of the white scattering particles of the diffusereflection layer 120 is to scatter the incident light. To achieve betterscattering effect, the particle diameters of the white scatteringparticles should cover the range of 0.2-0.5 μm. This is because typicalparticles have the highest reflectivity for light having a wavelengththat is about twice the diameter of the particles. The above particlediameter range corresponds to the wavelength range of 400 to 800 nm ofvisible light. Of course, the smaller the particle diameters of thewhite scattering particles, and the higher the packing density of thewhite scattering particles in the diffuse reflection layer, the betterthe scattering effect. But experiments show that at the same density,particles having diameters in the 0.2-0.5 μm range have the bestscattering effect. On the other hand, it is understood that for the samewhite scattering particles, the higher the mixing proportion of thewhite scattering particles, and the thicker the diffuse reflection layer120, the higher the reflectivity.

The diffuse reflection layer 120 can be affixed to the high thermalconductivity substrate 130 by adhesion. However, using an adhesionmethod, due to the existence of the adhesive, an interface layer ispresent between the diffuse reflection layer 120 and the high thermalconductivity substrate 130, which can interfere with the heat conductionfrom the diffuse reflection layer 120 to the high thermal conductivitysubstrate 130. Thus, preferably, the diffuse reflection layer 120 isdirectly sintered on the high thermal conductivity substrate 130. Thisway, the high thermal conductivity substrate 130 and the diffusereflection layer 120 have a strong binding force and high heatconductivity. When the adhesive of the diffuse reflection layer 120 isthe first glass powder, certain chemical binding occurs between theglass powder and the matrix of the ceramic high thermal conductivitysubstrate 130. The binding force between the two is much stronger thanthe binging force between glass and metal. Further, the thermalexpansion coefficients of glass and ceramic match better. Moreover,because the high thermal conductivity substrate 130 has relatively highthermal conductivity coefficient, it can conduct heat well, like metal.

Further, to take advantage of the strong binging force between theceramic substrate and the diffuse reflection layer 120, and to takeadvantage of the high thermal conductivity of metal substrates, the highthermal conductivity substrate 130 may be a composite structure ofceramic substrate coated with copper. The composite structure can berealized by forming a diffuse reflection layer on one surface of theceramic substrate, then coating the other surface of the ceramicsubstrate with copper. This can avoid oxidation and deformation of thecopper.

To obtain the above wavelength conversion device, an embodiment of thepresent invention provides a manufacturing method for the wavelengthconversion device. Refer to FIG. 2, which is a flow chart of amanufacturing process for a wavelength conversion device according to anembodiment of the present invention. As shown in FIG. 2, the methodincludes the following steps:

S11. Obtaining a high thermal conductivity substrate.

The high thermal conductivity substrate is one of an aluminum nitridesubstrate, a silicon nitride substrate, a silicon carbide substrate, aboron nitride substrate, and a beryllium oxide substrate.

S12. Obtaining a diffuse reflection layer.

The diffuse reflection layer includes white scattering particles forscattering an incident light. The diffuse reflection layer may be formedby mixing an adhesive such as silica gel with the white scatteringparticles and then forming a coating, or formed by sintering an adhesivesuch as glass powder with the white scattering particles, or formed bymixing sodium silicate with the white scattering particles and thenforming the layer by deposition.

S13. Obtaining a phosphor layer.

The phosphor layer includes a phosphor powder. The phosphor powder maybe adhered together by an adhesive. The adhesive may be silica gel,sodium silicate, glass powder, etc. The forming method depends on theadhesive used. For example, the phosphor powder may be mixed with asilica gel and then formed by coating, or mixed with sodium silicate andthen formed by deposition.

It should be noted that the order of performing steps S11, S12 and S13is not fixed.

S14. Sequentially stacking the phosphor layer, the diffuse reflectionlayer and the high thermal conductivity substrate and affixing them toeach other.

Step S14 may be performed after steps S11, S12 and S13. For example,after obtaining the phosphor layer, the diffuse reflection layer and thehigh thermal conductivity substrate, the three may be sequentiallyadhered together using adhesives. In such a method, the phosphor layerand the diffuse reflection layer may be formed using other substratesand then released from such substrates.

Step S14 may alternatively be performed concurrently with steps S11, S12and S13. For example, after obtaining the diffuse reflection layer andthe high thermal conductivity substrate, the two are adhered to eachother, and then the phosphor layer is obtained and is adhered to thediffuse reflection layer. Or, after obtaining the diffuse reflectionlayer and the phosphor layer, the two are first adhered to each other,and then the high thermal conductivity substrate is obtained and adheredto the diffuse reflection layer.

Also, the obtaining of the diffuse reflection layer and the adhering ofthe diffuse reflection layer with the high thermal conductivitysubstrate may be performed concurrently. For example, the diffusereflection layer may be directly formed on the surface of the highthermal conductivity substrate. Similarly, the obtaining of the diffusereflection layer and the adhering of the diffuse reflection layer to thephosphor layer may be performed concurrently. For example, the diffusereflection layer may be directly formed on the surface of the phosphorlayer. The obtaining of the phosphor layer and the adhering of thediffuse reflection layer to the phosphor layer may be performedconcurrently. For example, the phosphor layer may be directly formed onthe surface of the diffuse reflection layer.

The above manufacturing method can be used to make a wavelengthconversion device that includes stacked phosphor layer, diffusereflection layer and high thermal conductivity substrate.

In the above manufacturing method, each step may be implemented in manyways. To simplify the process, an embodiment of the present inventionprovides an optimized manufacturing method. Refer to FIG. 3, which is aflow chart of a manufacturing process for a wavelength conversion deviceaccording to another embodiment of the present invention. As shown inFIG. 3, the method includes the following steps:

S21. Obtaining a high thermal conductivity substrate.

Refer to the description of step S11 for an explanation of step S21.

S22: Sintering a diffuse reflection layer on the surface of the highthermal conductivity substrate. The diffuse reflection layer includeswhite scattering particles and a first glass powder.

In step S22, steps S12 and S14 in the method of FIG. 2 are carried outconcurrently. This simplifies the process; further, direct sinteringimproves the binding between the diffuse reflection layer and the highthermal conductivity substrate, and eliminates the interfacial thermalresistance caused by an adhesive.

To avoid damaging the high thermal conductivity substrate during thesintering of the diffuse reflection layer, the sintering temperatureshould be lower than the melting point of the high thermal conductivitysubstrate.

S23. Sintering a phosphor layer on the surface of the diffuse reflectionlayer. The phosphor layer includes a second glass powder and a phosphorpowder.

In step S23, steps S13 and S14 in the method of FIG. 2 are carried outconcurrently. This simplifies the process and eliminates the interfacialthermal resistance caused by an adhesive. Further, the phosphor layerincludes the second glass powder and a phosphor powder; compared tousing silica gel mixed with phosphor powder and then forming by coating,the second glass powder is more temperature resistant than silica gel.Also, the binding force between glass and glass is much stronger thanthat between glass and silica gel, so the binding between the diffusereflection layer and the phosphor layer is increased. Thus, sealing withglass powder is a preferred method. Of course, to prevent damaging thediffuse reflection layer during sintering of the phosphor layer, in thisstep, the sintering temperature T3 should satisfy the conditionT3≤Tf+400° C., where Tf is the softening temperature of the first glasspowder.

Further, it should be noted that step S22 does not have to be combinedwith step S23. For example, after step S22, the phosphor powder andsilica gel may be mixed and coated on the surface of the diffusereflection layer, and heated to form the layer. Or, the phosphor layermay be preformed and then adhered to the surface of the diffusereflection layer.

Further, the sintering sequence of the diffuse reflection layer and thephosphor layer does not have to be the same as described above; othersequence may be used. For example, the phosphor layer may be formed bysintering first, then the diffuse reflection layer is sintered on thesurface of the phosphor layer or the high thermal conductivitysubstrate, and last, the phosphor layer, the diffuse reflection layerand the high thermal conductivity substrate are stacked together andsintered again. Alternatively, the phosphor layer may be formed bysintering first, and a powder mixture of the first glass powder and thewhite scattering particles is coated on the surface of the high thermalconductivity substrate, and then the phosphor layer is placed to coverthe powder mixture, so that the phosphor layer, the powder mixture, andthe high thermal conductivity substrate are sequentially stacked, andare then sintered. Thus, while forming the diffuse reflection layer, thethree layers are sintered together. When the phosphor layer is sinteredfirst and the diffuse reflection layer is sintered later, to preventdamaging the phosphor layer while sintering the diffuse reflectionlayer, the sintering temperature T3 of the diffuse reflection layershould satisfy the condition T3≤Tf+400° C.

At room temperature, both the glass powder and the phosphor powder aresolid powders, and the compatibility of the two is not good. So in themixture, voids are present between the glass powder particles andphosphor powder particles, and the particles do not mix well to form anintegral mass. As a result, the phosphor layer obtained by sintering themixture tends to have air cavities and other detects. Due to thepresence of the air cavities, the excitation light may directly passthrough the phosphor layer through the air cavities, without excitingthe phosphor powder. To solve this problem, another embodiment isdisclosed. Refer to FIG. 4, which is a flow chart of a manufacturingprocess for a wavelength conversion device according to anotherembodiment of the present invention. As shown in FIG. 4, the methodincludes the following steps:

S31. Obtaining a high thermal conductivity ceramic substrate.

Refer to the description of step S11 for an explanation of step S31.

S32. Obtaining appropriate amounts of methyl silicone oil, whitescattering powder, and first glass powder.

Silicone oil is a mixture of polyorganosiloxanes of different degrees ofpolymerization. Methyl silicone oil, ethyl silicone oil, phenyl siliconeoil, methyl phenyl silicone oil, etc. are commonly used silicone oils.Silicone oil has certain viscosity, and has relatively small surfacetension, so it can easily wet the white scattering particles and thefirst glass powder and mix them into an integral mass. Among them,methyl silicone oil has relatively high complete break down temperature,high viscosity, and high thermal stability; its viscosity does notchange with temperature, which is advantageous for subsequent adjustmentof the viscosity of the slurry; and it will not easily experience phaseseparation. Thus, it is a preferred organic carrier. Of course, inaddition to silicone oil, other organic carriers that have sufficientviscosity and that can adhere the white scattering particles and thefirst glass powder into a mass of certain fluidity can be used. Examplesinclude glycol, PVB (polyvinyl butyral), ethyl cellulose, etc. Thesesubstances will decompose and evaporate after sintering or only leavesmall amounts of residues that have negligible impact on the scatteringeffect of the diffuse reflection layer.

The amount of the methyl silicone oil should be at least sufficient towet the white scattering particles and the first glass powder, so thatthe three mix to form an integral mass. The amounts of the whitescattering particles and the first glass powder can be determined basedon practical need, so long as the first glass powder can adhere thewhite scattering particles into an integral body in the subsequentsintering.

S33. Uniformly mixing the methyl silicone oil, the white scatteringparticles and the first glass powder to form a slurry of scatteringparticles.

To solve the problem that it is difficult to form the white scatteringparticles and the first glass powder into an integral mass, in thisstep, the white scattering particles, the first glass powder and themethyl silicone oil are mixed into an integral mass, such that themethyl silicone oil acts as a carrier for the white scattering particlesand the first glass powder, to obtain the scattering powder slurry.

To achieve uniform mixing, mechanical stirring may be used to performthe mixing. Here, step S33 may be performed after step S32, to mix thethree substances uniformly. Alternatively, steps S33 and S32 may beperformed concurrently, for example, by obtaining a certain amount ofthe first glass powder and white scattering particles, stirring thefirst glass powder and white scattering particles to mix them, meanwhileobtaining a certain amount of the methyl silicone oil, and graduallyadding it to the first glass powder and white scattering particles whilestirring.

S34. Coating the scattering particle slurry on the high thermalconductivity ceramic substrate.

The high thermal conductivity ceramic substrate is the carrier for thescattering particle slurry. The scattering particle slurry may be coatedon the high thermal conductivity ceramic substrate using a blade orother methods. Preferably, the scattering particle slurry may be coatedusing a screen printing method, which can make the thickness of thecoating of the scattering particle slurry on the high thermalconductivity ceramic substrate more uniform. As a result, thermal stressof the sintered layer is reduced.

S35. Sinter the high thermal conductivity ceramic substrate with thescattering particle slurry coating to form the diffuse reflection layer.

To sinter the scattering particle slurry, the sintering temperatureshould be above the softening point of the first glass powder in thescattering particle slurry; this way, the glass powder become a liquidphase, which helps to sinter it and the scattering particles into acompact diffuse reflection layer. But the temperature should not be toohigh, because otherwise certain amount of the white scattering powdercan chemically react with the glass powder which can impact the diffusereflection efficiency. It was discovered through experiments that asintering temperature T2 in the range Tf≤T2≤Tf+400° C. promotesformation, where Tf is the softening temperature of the first glasspowder.

It was discovered through experiments that, if the substrate coated withthe scattering particle slurry is directly sintered, the diffusereflection layer formed by sintered scattering particle slurry maycontain many air cavities. This is because the flash point of thesilicone oil is typically much lower than the softening point of theglass powder; when directly heating at a temperature near the softeningpoint of the glass powder, the silicone oil evaporates at too high aspeed, forming air cavities in the diffuse reflection layer. Therefore,in this embodiment, the scattering particle slurry is heated at a lowtemperature before sintering, so allow at least a part of the siliconeoil to slowly evaporate.

Preferably, the following step is performed before step S35: Heating thesubstrate coated with the scattering particle slurry at 200° C. for 0.2hours. When heated at 200° C. (which is 100° C. below the flash point ofthe methyl silicone oil which is 300° C.) for 0.2 hours, a large portionof the silicone oil will evaporate or decompose, and the residualsilicone oil can evaporate or decompose during sintering of thescattering particle slurry. Of course, it should be understood that thelower the heating temperature, the longer the heating time required toremove all the methyl silicone oil. Also, the longer the heating time,the smaller the amount of residual methyl silicone oil. To reduceheating time, the heating temperature for the scattering particle slurryand substrate may be increased; but to ensure that the methyl siliconeoil evaporates at a relatively slow speed, the heating temperatureshould be below 500° C. (which is 200° C. above the flash point of themethyl silicone oil which is 300° C.). For example, when the heatingtemperature is 500° C., after heating for 0.2 hours, more methylsilicone oil in the scattering particle slurry can evaporate, and thetime required to completely evaporate the methyl silicone oil is shorterthan that at a 200° C. heating temperature.

When other types of silicone oil is used to replace methyl silicone oil,to control the evaporation speed and evaporation amount of the siliconeoil, the heating temperature for the substrate coated with thescattering particle slurry should be controlled to be T1, such thatTb-100° C.≤T1≤Tb+200° C., where Tb is the flash point of the siliconeoil. The silicone oil will decompose and evaporate near its flash point.Of course, it is also possible to replace silicone oil with otherorganic additives, so long as the heating temperature for the substratecoated with the scattering particle slurry is controlled to be T1, suchthat Tb−100° C.≤T1≤Tb+200° C., where Tb is the complete break downtemperature of the organic additive.

In fact, if glycol replaces silicone oil to be mixed with the firstglass powder and the white scattering particles, even after a lowtemperature heating to remove the organic carried, the diffusereflection layer so formed will have many air cavities. This is becauseglycol is a pure substance; when heated to near its flash point, allglycol quickly evaporates, leaving the solid state white scatteringparticles and the first glass powder, and the volumes initially occupiedby the glycol that has since evaporated become air cavities. On theother hand, silicone oil is a mixture of polyorganosiloxanes ofdifferent degrees of polymerization; the polyorganosiloxanes ofdifferent degrees of polymerization have different flash points.Therefore, when the silicone oil is gradually heated up, thepolyorganosiloxanes of different degrees of polymerization willsequentially evaporate. This way, although some silicone oil isevaporated, the white scattering particles, the first glass powder andthe remaining silicone oil still has fluidity, so the white scatteringparticles and the first glass powder will move closer to each other tofill the volume left by the evaporated silicone oil. As a result, theformation of air cavities is reduced. Therefore, silicone oil is a morepreferred organic carrier.

It should be noted that during sintering, the silicone oil includingmethyl silicone oil is removed by decomposition and evaporation; a smallamount of silicon dioxide is generated when the silicone oil decomposes.This amount of silicon dioxide has virtually no impact on the scatteringeffect of the diffuse reflection layer.

Of course, in situations that are not sensitive to the amount of aircavities of the diffuse reflection layer, the step of low temperatureheating to remove the silicone oil can be omitted, and sintering can becarried out directly.

In fact, only when the heating temperature T1 is lower than thesintering temperature T2 in step S15, it is helpful to pre-remove thesilicone oil by low temperature heating, as it slows down theevaporation of the silicone oil. Therefore, T2 should be set to behigher than T1. However, when the temperatures T2 and T1 are close toeach other, the evaporation speeds of the silicone oil during the twoheating steps are not significantly different, so the effect of lowtemperature heating for removing the silicone oil is not significant.Therefore, here the temperatures T1 and T2 preferably meet the followingcondition: T2−T1≥100° C.

S36. Obtaining appropriate amounts of methyl silicone oil, phosphorpowder, and second glass powder.

The sequence of step S36 and the previous steps is not fixed and can beany sequence. In step S36, the function of the methyl silicone oil issimilar to that in step S32, the only difference being the othercomponents are the phosphor powder and the second glass powder.

S37. Uniformly mixing the methyl silicone oil, the phosphor powder, andthe second glass powder to form a slurry of phosphor powder.

Step S37 is similar to step S33, and the function of the methyl siliconeoil is to act as the carrier for the phosphor powder and the secondglass powder.

S38. Coating the phosphor powder slurry on the diffuse reflection layerwhich is on the high thermal conductivity substrate.

In step S38, the diffuse reflection layer is the carrier of the phosphorpowder slurry. The coating method is similar to that in step S34.

S39. Sinter the high thermal conductivity ceramic substrate with thephosphor powder slurry coating to form the phosphor layer.

The sintering process in this step is similar to that in step S35, onedifference being the sintering temperature satisfies: T3≤Tf+400° C.,where Tf is the softening point of the first glass powder. Also, a lowtemperature heating step may be similarly preformed to pre-remove thesilicone oil.

It should be noted that in this embodiment, when sintering the diffusereflection layer and the phosphor layer, an organic carrier, siliconeoil, is used as a carrier to make the mixing of the different substancesmore uniform. But it should be understood that the diffuse reflectionlayer and the phosphor layer are independent of each other, and theformation of each of them can use separate organic carrier to assist inthe formation.

Another embodiment of the present invention provides a light emittingdevice, including a wavelength conversion device as described in theabove embodiments, and further including an excitation light source forgenerating an excitation light. The phosphor absorbs the excitationlight to generate a converted light. The diffuse reflection layerscatter-reflects the converted light or a mixed light of the convertedlight and unabsorbed excitation light. The high thermal conductivitysubstrate dissipates the heat conducted through the diffuse reflectionlayer into the air.

The above descriptions disclose the embodiments of the presentinvention, but do not limit the scope of the invention. Thus, it isintended that the present invention cover modifications and variationsthat come within the scope of the appended claims and their equivalents,as well as direct or indirect applications of the embodiments in otherrelated technical fields.

1.-6. (canceled)
 7. A manufacturing method for a wavelength conversiondevice, comprising: A. obtaining a high thermal conductivity substrate,which is selected from: an aluminum nitride substrate, a silicon nitridesubstrate, a silicon carbide substrate, a boron nitride substrate, and aberyllium oxide substrate; B. obtaining a diffuse reflection layer,which includes white scattering particles for scattering an incidentlight; C. obtaining a phosphor layer, which includes a phosphor powder;and D. sequentially stacking the phosphor layer, the diffuse reflectionlayer and the high thermal conductivity substrate and affixing them toeach other.
 8. The manufacturing method of claim 7, wherein step B andstep D include: sintering the diffuse reflection layer on a surface ofthe high thermal conductivity substrate, wherein the diffuse reflectionlayer includes white scattering particles and a first glass powder,wherein a sintering temperature is lower than a melting point of thehigh thermal conductivity substrate, and affixing the phosphor layer ona surface of the diffuse reflection layer on the surface of thesubstrate.
 9. The manufacturing method of claim 7, wherein step B, stepC and step D include: sintering the diffuse reflection layer on asurface of the high thermal conductivity substrate, wherein the diffusereflection layer includes the white scattering particles and a firstglass powder, wherein a sintering temperature is lower than a meltingpoint of the high thermal conductivity substrate, and sintering thephosphor layer on a surface of the diffuse reflection layer on thesurface of the substrate, wherein the phosphor layer includes a secondglass powder and the phosphor powder, and wherein a sinteringtemperature is T3≤Tf+400° C., where Tf is a softening point of the firstglass powder.
 10. The manufacturing method of claim 8, wherein the stepof sintering the diffuse reflection layer on the surface of the highthermal conductivity substrate includes: B1. obtaining the whitescattering particles, the first glass powder, and an organic carrier;B2. mixing the white scattering particles, the first glass powder, andthe organic carrier to obtain a slurry of the scattering particles; B3.coating the slurry of the scattering particles over the high thermalconductivity substrate; and B4. sintering the high thermal conductivitysubstrate which has been coated with the slurry of the scatteringparticles to obtain the diffuse reflection layer.
 11. The manufacturingmethod of claim 9, wherein the step of sintering the phosphor layer onthe surface of the diffuse reflection layer on the surface of thesubstrate includes: C1. obtaining the second glass powder, the phosphorpowder, and an organic carrier; C2. mixing the second glass powder, thephosphor powder, and the organic carrier to obtain a slurry of thephosphor powder; C3. coating the slurry of the phosphor powder over thesurface of diffuse reflection layer of the high thermal conductivitysubstrate; and C4. sintering the high thermal conductivity substratewhich has been coated with the slurry of the phosphor powder to obtainthe phosphor layer, wherein a sintering temperature is T3≤Tf+400° C.,where Tf is a softening point of the first glass powder.
 12. Themanufacturing method of claim 10, further comprising, between step B3and step B4: heating the high thermal conductivity substrate which hasbeen coated with the slurry of the scattering particles at a temperatureT1 for over 0.2 hours, wherein Tb−100° C.≤T1≤Tb+200° C., where Tb is acomplete break down temperature of the organic carrier.
 13. (canceled)